The present invention relates to a transmission unit for a vehicle.
Transmission units for vehicles are known which comprise gear changes with gearing adapted to vary the transmission ratio in a discrete manner, and a clutch adapted to transmit motion from the vehicle engine to the input shaft or primary shaft of the gear change. Transmission units of an automatic or servo-assisted type are in particular known in which the transmission ratio is varied and the clutch engaged/disengaged by actuators of electric, pneumatic or hydraulic type operated and controlled by an electronic control unit of the vehicle.
As is known, during each gear change, it is necessary to eliminate the relative speed difference between the gears to be coupled with the clutch disengaged. For this purpose, rather complex transmission units are known, which are costly and of considerable size, comprising a plurality of synchroniser rings associated with each gear of the gear change.
As an alternative, it is known to use gear changes provided with a single braking synchronisation member.
The braking member is housed in the structure of the gear change and is adapted to reduce the speed of the primary shaft, with the clutch disengaged, when a gear with a transmission ratio greater than the current gear is being selected.
Transmission units of the type described above are not very satisfactory as they are also relatively complex, costly and bulky. In order to actuate and control the braking member it is necessary to provide a dedicated actuator of electric, pneumatic or hydraulic type, with the relative control devices, for instance supply ducts and electrovalves in the case of an oil-hydraulic actuator.
There is a further need to maintain the vehicle stationary on a sloping road without the driver having continuously to depress the brake pedal. In this respect it is known to use stopping devices associated with the braking unit of the vehicle in order to keep the wheels braked, with the clutch disengaged, and in particular, rather complex automatic stopping devices controlled by a relative electronic control unit.
The object of the present invention is to provide a transmission unit for a vehicle, which makes it possible to remedy the above-mentioned problems in a simple and economic way.
The present invention therefore relates to a transmission unit for a vehicle comprising a clutch unit comprising a motion input member adapted to be coupled to a motor-driven shaft and a motion output shaft adapted to be connected to an input shaft of a gear change, first actuator means for controlling the clutch unit, braking means to brake the input shaft of the gear change, and second actuator means to control the braking means, characterised in that the first and second actuator means comprise a single actuator unit common to the clutch unit and the braking means in order to actuate these braking means at least when the clutch unit is in a disengaged condition.